Field of the Invention
The present invention relates to an image processing technology for assisting image processing on images of an eye, and more particularly, to an image processing apparatus, an image processing method, and a program for performing image processing using a tomographic image of an eye.
Description of the Related Art
An ophthalmic tomographic image photographing device such as an optical coherence tomography (OCT) device enables three-dimensional observation of an internal state of a retina. In recent years, this ophthalmic tomographic image photographing device has become popular for its capability of appropriately diagnosing diseases. The amount of OCT tomographic information is huge, and hence it is very inefficient to check the tomographic information piece by piece. To relieve the burden of doctors on OCT-based diagnosis, therefore, there is a demand to establish a computer-aided diagnosis (CAD) technology. For example, Japanese Patent Application Laid-Open No. 2011-110158 describes that characteristic amounts on a fundus image are detected at two points thereof, a reference coordinate system for a projection image is determined on the basis of the two points, and the reference coordinate system is converted to a display coordinate system to display the projection image corresponding to the display coordinate system. Japanese Patent Application Laid-Open No. 2011-110158 proposes a scheme of displaying OCT analysis results in accordance with the display coordinate system.
However, Japanese Patent Application Laid-Open No. 2011-110158 fails to describe processing that is performed in displaying a fundus image and a tomographic image. In general, a tomographic image is expanded and displayed two-dimensionally. When a tomographic image and a fundus image are displayed with a single corresponding point taken as a reference, therefore, the tomographic image and the fundus image match with each other at the origin of the reference coordinate system, but as the distance from the origin of the reference coordinate system is longer, the deviation amount becomes larger. This phenomenon is described referring to schematic diagrams of FIGS. 16A to 16C. FIG. 16A illustrates a fundus image. An arbitrary point 1401 lies on a line extending vertically on the fundus image and passing nearly through the center of the fundus image. An arbitrary point 1402 lies in a macula present on the line. An arbitrary point 1403 is a point on a papilla present on the line. A distance 1404 and a distance 1405 are vertical distances from the arbitrary point 1402 to the arbitrary point 1401 and from the arbitrary point 1402 to the arbitrary point 1403, respectively. FIG. 16B illustrates the cross section of an eye corresponding to the line containing points 1401, 1402 and 1403 at the fundus. FIG. 16C illustrates a tomographic image acquired by OCT-based measurement of the same vertical line. The OCT tomographic image is normally expanded and displayed two-dimensionally with the arbitrary point 1402 as the reference point, that is, the origin. A distance 1406 represents a deviation amount of the actual arbitrary point 1401 on the tomographic image from the arbitrary point 1401 on the fundus image. A distance 1407 represents a deviation amount of the actual arbitrary point 1403 on the tomographic image from the arbitrary point 1403 on the fundus image. As the distances 1404 and 1405 from the display reference point are longer, the deviation between the fundus image and the tomographic image is greater.
When a point of interest (e.g., point which is suspected to be a lesion) is other than the reference point, therefore, an inspector carries out diagnosis by referring to a screen in which the tomographic image and the fundus image do not match with each other. This makes it difficult to support diagnosis of a variety of diseases, and hinders prompt diagnosis.